JPH05102047A - Diamond substrate and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture and provide large-area single crystal diamond substrates suitable for semiconductor devices and the like in a large quantity and at a low cost. CONSTITUTION:A diamond substrate having a single crystal diamond layer grown on a carbon atom face of a single silicon carbon substrate by preparing a carbon substrate whose growing surface is a carbon atom face with appearance of only carbon atoms out of a crystal face of single crystal silicon carbide and by growing a single crystal diamond layer by a vapor composition method such as CVD on the carbon atom face of this growing surface.

Description

Detailed Description of the Invention

[0001]

The present invention relates to various semiconductor devices such as transistors and sensors, heat sinks and insulating films,
Alternatively, the present invention relates to a diamond substrate useful as a high-hardness coating used for a cemented carbide tool and a method for producing the diamond substrate.

[0002]

2. Description of the Related Art Diamond is a cubic crystal in which carbon is covalently bonded, is a substance having the highest hardness, and at the same time has many excellent properties. For example, diamond has a very wide band gap and can be made into a semiconductor by doping impurities, so that it can be used as a semiconductor device such as a transistor or a sensor or a short-wavelength light-emitting element that operates stably even at high temperature. It is considered. Further, since diamond has a high thermal conductivity, it is expected to be used as a heat sink or the like.

Attempts to synthesize diamond have been made for a long time, and in the 1950s, it was successful to synthesize granular diamond by a high pressure synthesis method. However, as described above, when used as a semiconductor device or the like, a high-purity and large-area single crystal is desired, but the diamond currently obtained by the high-pressure synthesis method is only a plate-like or granular crystal of about several mm. is there. Further, the high-pressure synthesis method requires a very expensive high-pressure generator, so that the unit price of a single crystal becomes extremely expensive.

On the other hand, in order to form a diamond thin film suitable for semiconductor devices and the like, synthesis from the gas phase has also been actively studied, and microwave plasma CVD method, high frequency plasma CVD method, hot filament CVD method, ECR plasma CVD method. It has also been reported that diamond has been successfully synthesized by a vapor phase synthesis method such as an arc discharge plasma jet CVD method.

However, a single crystal diamond thin film can be obtained by the above vapor phase synthesis method from natural diamond, or single crystal diamond synthesized by a high pressure synthesis method or a zinc blende type boron nitride single crystal (cBN). ) Is limited to the substrate. Therefore, the substrate itself for diamond growth is extremely expensive, and it is difficult to obtain a large-area substrate. Therefore, it is necessary to mass-produce an inexpensive large-area single crystal diamond substrate suitable for applications such as semiconductor devices. I couldn't.

Besides diamond and cBN mentioned above, silicon (Si) and aluminum oxide (Al ₂ O ₃ ) are used as substrates for diamond growth. Or, at present, only diamond-like carbon films are obtained.

[0007]

In view of the above conventional circumstances, the present invention grows diamond by a vapor phase synthesis method using a large-sized substrate which is inexpensive and has a large area suitable for use in semiconductor devices and the like. It is an object of the present invention to manufacture and provide a crystalline diamond substrate in large quantities and at low cost.

[0008]

In order to achieve the above-mentioned object, in the present invention, a substrate having a carbon atom plane in which only carbon atoms appear among the crystal planes of single crystal silicon carbide as a growth surface is prepared. A diamond substrate is manufactured by a method characterized by growing a single crystal diamond layer on a carbon atom plane of a growth surface by a vapor phase synthesis method.

The diamond substrate produced by the method of the present invention is a substrate made of single crystal silicon carbide,
This substrate has a single crystal diamond layer grown on a carbon atom plane in which only carbon atoms appear.

[0010]

[Function] Silicon carbide (SiC) substrates have been used in the past, but polycrystalline SiC is often used, and even when single-crystal SiC is used, it has not been determined which crystal plane is to be the surface for diamond growth. In all cases, it was difficult to stably obtain a single crystal diamond layer.

The substrate used for the growth of the diamond layer in the present invention is a single crystal silicon carbide, and the carbon atom plane in which only carbon atoms appear is the surface for diamond growth. It was confirmed that the single crystal diamond layer was always epitaxially grown on the surface by using the carbon atomic plane of the single crystal SiC substrate as the surface for diamond growth. It is considered that this is because the carbon atoms on the surface of the substrate and the carbon atom-containing active species in the vapor phase were easily chemically bonded to each other, which promoted the diamond nucleus growth.

Crystal structures of single crystal SiC include those belonging to the cubic system and those belonging to the hexagonal system. Cubic
SiC is a zinc blende type structure in which half of the carbon atoms of the diamond structure are alternately replaced by silicon atoms, and only carbon atoms or only silicon atoms appear on the (100) and (111) faces of the crystal planes. Hexagonal system SiC has a wurtzite structure, and only carbon atoms or silicon atoms appear on the (001) plane of the crystal planes. However, the cubic system (1
Since it is difficult to cut out the (00) plane accurately and smoothly, the (111) plane in the cubic system and (0) in the hexagonal system
It is preferred to use the 01) plane.

Whether the cubic (111) plane or hexagonal (001) plane is a carbon atom plane in which only carbon atoms appear or a silicon atom plane in which only silicon atoms appear. Can be determined by the surface condition (degree of etching) by etching with potassium nitrate or the like, that is, the carbon atom surface is more easily etched than the silicon atom surface, and a coarse eclipse image appears and the surface becomes rough. It is also possible to identify the carbon atom surface by the difference in the reflection intensity of the diffraction line by X-ray diffraction.

Cubic SiC has a lattice constant of 0.43596 nm.
Thus, even when compared with the lattice constant of Si of 0.5430 nm, it is close to the lattice constant of 0.3543 nm of cubic diamond. Therefore, it is considered that diamond is more likely to grow epitaxially on the carbon atomic planes of the cubic SiC substrate.

The single crystal SiC substrate used in the present invention can be manufactured by a known method such as a sublimation method, an Acheson method or a thermal CVD method. Single-crystal SiC substrates manufactured by these methods are, compared to conventional natural or synthetic diamond or cBN,
It has the advantages of easy synthesis, large area, and low price.

Hexagonal S produced by sublimation method or Acheson method
In the case of iC, a (001) plane is cut out from an ingot to obtain a single crystal hexagonal SiC substrate. or,
In the case of cubic system SiC, by growing it on the (111) plane of a Si substrate or the (001) plane of a hexagonal system SiC substrate by a thermal CVD method or the like, a cubic crystal of a single crystal of the (111) plane is obtained. SiC substrate is obtained. Then, for each substrate, the carbon atomic planes may be identified or confirmed by etching or the like as described above. However, the Si substrate used as the substrate for the thermal CVD method or the like may be removed later and only the single crystal SiC as the self-supporting film may be used as the substrate for diamond growth, or it may be directly used as the substrate for diamond growth without removal. It is possible.

In the present invention, the single crystal diamond layer grown on the single crystal SiC substrate is made of a single crystal containing a good quality single crystal or twin crystal. Therefore, the surface of the diamond layer is extremely smooth, and the surface roughness (R _max ) measured by a surface roughness meter is about 5% or less of the film thickness. The thickness of the single crystal diamond layer is preferably 10 μm or less in order to prevent warpage of the diamond substrate due to the difference in thermal expansion coefficient from the single crystal SiC substrate. However, single crystal SiC
When the substrate is later removed and only the single crystal diamond layer is used as a self-supporting film, the thickness may exceed 10 μm.

Further, the single crystal diamond layer may be either a non-doped layer or a doped layer depending on its use. Especially when it is used as an active layer of a semiconductor device, it is of p-type or n-type doped with impurities such as boron and phosphorus. Use semiconductor.

[0019]

Example 1 A hexagonal SiC single crystal ingot was manufactured by a known sublimation method, and a plane orientation (0
In 01), a hexagonal SiC single crystal wafer having a diameter of 1 inch was cut out. Both sides of the SiC single crystal wafer of this plane orientation (001) were etched with potassium nitrate, and it was confirmed from the state of the etched surface that this plane was a carbon atom plane. Then, the carbon atom surface was polished and washed with an acid and an organic solvent to obtain a substrate for diamond growth.

The growth substrate 1 is placed in a reaction chamber 2 of the microwave plasma CVD apparatus shown in FIG. 1, and CH ₄ gas 1 is used as a reaction gas in the reaction chamber 2 which is evacuated.
Sccm and 100 sccm of H ₂ gas were simultaneously introduced to adjust the pressure inside the reaction chamber 2 to 7 × 10 ³ Pa. In this state, 400 W microwaves were supplied from the 2.45 GHz microwave generator 3 through the waveguide 4 into the reaction chamber 2 to form plasma of the source gas on the growth substrate 1. At this time, the substrate temperature was 1070 K, and a diamond layer was formed on the growth substrate 1 to a thickness of 1 μm.

As a result of analyzing the obtained diamond layer by a high-speed reflection electron diffraction method (hereinafter abbreviated as RHEED method), it was found to be a (111) plane of a single crystal diamond containing a small amount of twin crystals. Also, the surface roughness of this diamond layer
Rmax was 35 nm, which was found to be an extremely smooth surface.

For comparison, the plane orientation (1
00) hexagonal single crystal SiC substrate and plane orientation (111)
An attempt was made to form a diamond layer in the same manner as in Example 1 except that the single crystal Si mirror-finished substrate was used. However, in each case, only a very small amount of diamond particles were observed. Couldn't get.
In addition, the grain size of the single crystal Si mirror surface substrate with the above-mentioned plane orientation (111) is 20
A diamond layer was formed in the same manner as in Example 1 after being scratched with diamond abrasive grains of -40 μm, and the thickness was 1 μm.
Although a diamond layer was obtained, a spotty ring pattern was obtained by the RHEED method, and it was confirmed that the diamond layer was polycrystalline diamond.

[0023]

Example 2 On a single crystal Si substrate having a plane orientation (111),
SiC was formed by a known thermal CVD method. This SiC is RH
It was found by the EED method that this was a cubic SiC single crystal with a plane orientation (111). Then, this was immersed in hydrofluoric nitric acid to remove Si by etching to obtain a free-standing SiC film. The SiC single crystal of this plane orientation (111) was confirmed to be a carbon atom plane in the same manner as in Example 1, and the carbon atom plane was polished and washed with an acid and an organic solvent to grow diamond. It was used as a substrate.

The growth substrate 1 is placed in the reaction chamber 2 of the hot filament CVD apparatus shown in FIG.
While heating the hot filament 5 installed facing to 2273K, CH ₂ gas 2sccm and H ₂ gas 200sccm are simultaneously introduced as reaction gas into the evacuated reaction chamber 2 to increase the pressure in the reaction chamber 2. Adjusted to 1 × 10 ⁴ Pa.
The distance between the substrate 1 and the hot filament 5 was 5 mm, and the back surface of the substrate was water-cooled so that the substrate temperature was 1120K. Thus, a 10 μm thick diamond layer was formed on the growth substrate 1. As a result of analyzing the obtained diamond layer by the RHEED method, it was found to be a (111) plane of single crystal diamond containing a small amount of twin crystals.

For comparison, the plane orientation (1
10) Cubic single crystal SiC substrate and plane orientation (111)
An attempt was made to form a diamond layer in the same manner as in Example 2 except that the single crystal Si mirror surface substrate was used. However, in each case, only a part of diamond particles were observed. Couldn't get.
In addition, the grain size of the single crystal Si mirror surface substrate with the above-mentioned plane orientation (111) is 20
A diamond layer was formed in the same manner as in Example 2 after being scratched with diamond abrasive grains of -40 μm, and the thickness was 10 μm.
A diamond layer of m was obtained, but it was confirmed by RHEED method that it was polycrystalline diamond.

[0026]

Example 3 In the same manner as in Example 1, both sides of a SiC single crystal wafer having a plane orientation (001) cut out from an ingot of a hexagonal SiC single crystal produced by a known sublimation method were etched with potassium nitrate to form an etched surface. From this state, it was confirmed that this surface was a carbon atom surface, and this carbon atom surface was polished and washed with an acid and an organic solvent to obtain a substrate for diamond growth.

Magnetic field microwave plasma CV shown in FIG.
The growth substrate 1 is placed in the reaction chamber 2 of the D apparatus, and CH 2 is used as a reaction gas in the reaction chamber 2 which is evacuated.
₄ gas 4 sccm and H ₂ gas 200 sccm were simultaneously introduced to adjust the pressure inside the reaction chamber 2 to 10 Pa. In this state, a microwave of 400 W is supplied from the 2.45 GHz microwave generator 3 through the waveguide 4 into the reaction chamber 2 and, at the same time, a magnetic field of 875 G is applied by the magnetic field generating coil 6 to generate a magnetic field. A source gas plasma was formed on the growth substrate 1 below. At this time, the substrate temperature was 1000 K, and a diamond layer was formed on the growth substrate 1 to a thickness of 10 μm. As a result of analyzing the obtained diamond layer by the RHEED method, it was found to be a (111) plane of single crystal diamond containing a small amount of twin crystals.

For comparison, the plane orientation (1
00) hexagonal single crystal SiC substrate and plane orientation (001)
An attempt was made to form a diamond layer in the same manner as in Example 3 except that the single crystal Al ₂ O ₃ mirror substrate of No. 1 was used, but in each case, only a part of diamond particles were observed. No crystalline diamond layer could be obtained. Further, after the single crystal Al ₂ O ₃ mirror-finished substrate having the above-mentioned plane orientation (001) was scratched with diamond abrasive grains having a grain size of 20 to 40 μm, a diamond layer was formed in the same manner as in Example 3 to obtain a diamond having a thickness of 10 μm. A layer was obtained, which was confirmed to be polycrystalline diamond by the RHEED method.

[0029]

According to the present invention, a large area single crystal diamond substrate suitable for applications such as semiconductor devices can be manufactured and provided in large quantities at low cost.

[Brief description of drawings]

FIG. 1 is a microwave plasma CV used for implementing the present invention.
It is a schematic explanatory drawing of a D apparatus.

FIG. 2 is a schematic explanatory view of a hot filament CVD apparatus used for carrying out the present invention.

FIG. 3 is a schematic explanatory diagram of a magnetic field microwave plasma CVD apparatus used for carrying out the present invention.

[Explanation of symbols]

 1 Growth Substrate 2 Reaction Chamber 3 Microwave Generator 4 Waveguide 5 Hot Filament 6 Magnetic Field Generation Coil

Claims (2)

[Claims] 1. A diamond substrate having a substrate made of single-crystal silicon carbide and a single-crystal diamond layer grown on a carbon atom plane in which only carbon atoms appear in the crystal plane of the substrate. 2. A substrate having a growth surface which is a carbon atom surface in which only carbon atoms are present among crystal faces of single crystal silicon carbide is prepared, and a single crystal is formed on the growth surface by the vapor phase synthesis method. A method for manufacturing a diamond substrate, which comprises growing a diamond layer.